Image forming apparatus with fixer temperature control

ABSTRACT

An image forming apparatus comprises includes a feeder means and recorder. The feeder feeds a sheet of recording paper to a predetermined position in response to a spare paper feed signal instructing the feeding of the sheet of recording paper to the predetermined position preliminarily, and then feeds the sheet of recording paper being stopped at the predetermined position again in response to a record request signal. The recorder records an image on the sheet of recording paper fed by the feeder means through an electrophotographic process. The recorder means starts preparation to execute the electrophotographic process upon receiving the spare paper feed signal. As a result, throughput is increased without causing other problems.

This application is a continuation of application Ser. No. 07/974,503,filed Nov. 12, 1992, which is a division of application Ser. No.07/703,298, filed May 20, 1991, U.S. Pat. No. 5,274,402.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus forconverting character or figure information into bit mapped information(pixel information) and forming an image based on the convertedinformation.

Also, the present invention relates to an image recording apparatus suchas a laser printer, for example, which has a spare paper feedingfunction.

In this specification, the term "spare paper feeding function" means afunction of starting to feed a spare sheet of recording paper prior toreception of a signal indicating the start of recording.

2. Related Background Art

Electrophotographic printers are able to produce prints with highresolution and high quality. Therefore, various types ofelectrophotographic printers such as laser printers, LED printers andliquid crystal printers have recently been developed and becomewidespread. By utilizing a high quality feature, those printers are usedto output complex figures and pictures.

A controller (e.g., a postscript controller) for processing compleximage data covering one page of printed sheet requires an image memory(hereinafter referred to as a page memory) with a capacity correspondingto one page at a minimum. To print a sheet of A4 size with resolution of300 dpi, for example, a page memory having a capacity as large as 1Mbyte is required.

There is a large amount of image information to be processed by suchhigh quality printers. Accordingly, image data to be handled by memorydevices of computers and other systems for image processing equipmentare often in the form of coded data or programmed data rather than rawraster image data.

The performance of page printers is determined by how fast coded imageinformation of one page is converted into raster image information ofone page before printing.

One example of a control form in page printers of prior art is asfollows.

FIG. 1 shows a section of a laser beam printer as typical a one of pageprinter. FIG. 2 is a schematic block diagram of a control circuit in thetypical laser beam printer. In FIG. 2, reference numeral 25 representsan information processing apparatus (such as a personal computer or workstation, for example) external to the laser printer. Reference numeral27 denotes an external interface (such as Centronics or RS232C, forexample) which delivers coded image information (such as ASCII code, forexample, hereinafter referred to as coded information) to the laserprinter. The coded information is received by an interface circuit 18 inthe laser printer. A microprocessor 17 receives the coded information,received by the interface circuit 18, through an internal bus 28. Theinternal bus 28 comprises a collection of a data bus, an address bus anda control bus. The microprocessor 17 is operated in accordance with acontrol program stored in a memory 21. The memory 21 is a non-volatileROM.

The microprocessor 17 processes the coded information obtained throughthe interface circuit 18 to some extent and stores it in a memory 19.Thus, the memory 19 is a RAM for storing the coded information. Themicroprocessor 17 sequentially stores the coded information externallyreceived into the RAM 19 and, at the same time, converts the codedinformation into image information representing a dot image, followed bystoring it in a RAM 20. Thus, the RAM 20 is an image data store memory(bit map memory). Denoted by 22 is a DMA controller serving to read outthe data stored in the RAM 20 and deliver the read data to a rasterconversion circuit 24.

The DMA controller 22 may exclusively use the internal bus 28independently of the microprocessor 17. When it is detected that theimage data stored in the RAM 20 has reached an amount corresponding toone page (i.e., all the coded data of one page have been converted intothe image data), the microprocessor 17 sets the DMA controller 22 in anactive state. The DMA controller 22 exclusively uses the internal busalternately with the microprocessor 17. Upon a request from the rasterconversion circuit 24, the DMA controller 22 sequentially reads theimage data out of the RAM 20 and delivers the read data to the rasterconversion circuit 24. The raster conversion circuit 24 converts theparallel image data received from the DMA controller 22 into serialimage data. Then, in synchronism with a horizontal synch signal, theserial image data are outputted to a laser driver (not shown) in amechanical control unit 26 for modulating a laser beam.

Mechanical control in the laser printer will be described below withreference to FIG. 1. In FIG. 1, reference numeral 1 represents a body ofthe laser printer. After developing the coded data of one page andstoring the image data in the memory 20, the microprocessor 17 rotates afeed motor (not shown) through an I/O driver 23. This starts rotating aphotosensitive drum 2, a primary charge roller 5, a development roller7, a transfer roller 10, a fixer roller 15A, and a discharge roller 16.The feed motor is controlled in its rotation by the mechanical controlunit 26.

Reference numeral 3 represents a laser scanner which houses a laser scanmirror, a laser scan motor, a laser emitting element, and a laser drivecircuit therein. The I/O driver 23 serves to rotate not only the feedmotor but also the laser scan motor within the laser scanner 3. The I/Odriver 23 also sequentially applies high voltage biases to the primarycharge roller 5, the development roller 7 and the transfer roller 10.Further, the I/O driver 23 turns on a clutch mounted on a paper feedroller 12 to feed sheets of transfer material 13 such as paper stackedin a paper cassette 14 one by one. The sheet of transfer material 13thus fed is once stopped by a resist roller 11. Then, the mechanicalcontrol unit 26 informs the I/O driver 23 that the fed sheet of transfermaterial 13 has reached the resist roller 11. At the time the sheet oftransfer material 13 is stopped by the resist roller 11, themicroprocessor 17 sets the DMA controller 22 in an active state.Subsequently, the serial image data are delivered from the rasterconversion circuit 24. The delivered serial image data are inputted tothe laser scanner 3 so that a laser beam modulated by the image datairradiates to the photosensitive drum 2. This builds a latent image onthe surface of a photoreceptor, the latent image being visualized into atoner image by a development unit 6.

The sheet of transfer material 13 once stopped by the resist roller 11starts to be fed again by the resist roller 11, and the toner image istransferred to the sheet of transfer material 13 by the transfer roller10. The sheet of transfer material 13 with toner deposited thereon isfixed under heating by the fixer roller 15A and, thereafter, it isdischarged by the discharge roller 16 externally of the printer body.The remaining toner that has not been transferred to the sheet oftransfer material 13 by the transfer roller 10 is collected by a cleaner9.

While the fixer roller 15A is generally adjusted to a predeterminedtemperature, i.e., a temperature for printing (during the fixingoperation), it may be also adjusted to a lower setting temperature,i.e., a standby temperature, other than that printing temperature. Thisaims to prevent a temperature rise in the printer, reduce electric powerconsumption, etc.

In this way, the coded information given from the external informationprocessing apparatus is printed as image information on the sheet ofpaper.

When printing data in an amount corresponding of plural pages, theprinting is performed in accordance with the timed relationship shown inFIG. 3. Referring to FIG. 3, the microprocessor 17 starts reception ofthe coded information at the timing (a). Simultaneously, themicroprocessor 17 starts the image development and stores the image datain the memory 20. After terminating the reception of the coded data forthe first page at the timing (b), the microprocessor 17 successivelystarts reception of the coded information at the timing (c). If imagedevelopment for the first page is completed at the timing (d), the feedmotor is rotated at the timing (f) to perform the paper feedingoperation. Then, the resist roller 11 is driven at the timing (g) andreading of the image data by the DMA controller 22 is started at thetiming (h). Simultaneously, the serial image data are produced by theraster conversion circuit 24 and laser exposure is started at the timing(h). Afterward, the laser exposure for the first page is completed atthe timing (i). Since the reception of the coded information for thesecond page has already been completed at the timing (e), the imagedevelopment for the second page is also started at the timing (i). Afterthat, the second page is printed following the same sequence as thefirst page,

As will be seen from FIG. 3, the periods of (a) to (d) and (i) to (j) ofthe image development are completely independent of the period of (h) to(i) for reading the image data (also the period for the laser exposure),with no overlapping periods therebetween. This is because the imagememory has a capacity corresponding to only one page.

With the foregoing control method, no access is made to the image memory20 during the period of (f) to (h) (or the period of (k) to (m)).Accordingly, the throughput (the number of sheets printed per unit time)is lowered in laser beam printers of the type that the distance betweenthe paper feed roller 12 and the resist roller 11 is very long.Providing the image memory with a capacity corresponding to two pagesmakes it possible to overlap the period of the image development and theperiod of reading the image data with each other, and thus increase thethroughput. In this case, however, the memory cost is doubled.

To solve the aforementioned disadvantage, the following control methodcould be envisaged.

With this method, at the time the microprocessor 17 receives the codedinformation of one page from the external information processingapparatus 25 such as a host computer, the feeding operation for thesheet of transfer material 13 such as paper is started and then stoppedat a predetermined position in a standby state. Afterward, at the timethe microprocessor 17 has completely finished the development of thecoded information into the image data representing the dot image, theimage data representing the dot image are sequentially transferred asthe serial image data to the mechanical control unit 26, so that thelaser beam is modulated to expose the surface of the electrophotographicphotosensitive drum 2. At the same time, in synchronism with theexposure image, the sheet of transfer material 13 starts to be fed againfrom the standby state.

However, the above control method raises a problem discussed below whenpracticed while implementing usual temperature adjustment in two modes;i.e., a standby temperature and a printing temperature.

When the process shifts into the printing operation after completion ofthe image development, a certain period of time is required for thefixer roller 15A to reach the printing temperature.

For example, assuming that the fixer roller 15a used comprises analuminum-made core with a wall thickness of 2 mm, assuming that theroller's outer diameter is 25 and the roller's length is 260 mm and theroller has a fluoroplastic layer of 30 μm or thereabout coated on thecore assuming that a halogen heater is used in the fixer roller 15Ahaving output power of 400 W, and assuming that the standby temperatureis 165° C., and the printing temperature is 180° C., it takes about 6seconds for the fixer roller 15A to heat from the standby temperature tothe printing temperature.

Naturally, the above period of time is prolonged as the weight of theroller is increased, the heater output power is reduced, and thedifference between the standby temperature and the printing temperaturebecomes large.

If the temperature adjustment mode of the fixer roller 15A is shifted toa lower temperature for the standby state to wait for the end of theimage development as mentioned above, the period of time required to beprepared for the next printing operation would be dependent on theperiod of time required for the fixer roller 15A to reach a statecapable of starting the fixing operation. This results in the problem oflowering throughput in terms of the sheets of transfer material printedper unit time.

Another laser beam printer of the prior art is arranged as shown in FIG.4. Referring to FIG. 4, denoted by 201 is a photoreceptor drum as acarrier for an electrostatic latent image, 202 denotes a charge rollerfor uniformly charging the photoreceptor drum, 207 denotes a scannermotor for scanning a laser beam 206 over the photoreceptor drum 201,203is a developer for developing the electrostatic latent image, created bya laser beam 206 on the photoreceptor drum 201, using toner, 204 denotesa transfer roller for transferring a toner image to a sheet of printpaper, 205 denotes a cleaner for removing the non-transferred tonerremaining the photoreceptor drum 201, 208 denotes a fixer for fixing thetoner on the sheet of print paper thereto, 209 is a paper feed roller,211 denotes a pre-resist sensor, and 210 denotes a resist roller forsynchronizing the paper feeding and the image production.

A print control system of the printer thus arranged is shown in FIG. 3.

Denoted by 300 is a printer controller for developing an image codesignal from a host computer or the like into a dot signal, outputting aprint request signal and a spare paper feed signal to a printer enginecontrol unit 301, and further delivering the developed dot data. 301 isa printer engine control unit for controlling communication with theprinter controller 300 and various components of the engine. A ROM ofthe printer engine control unit stores a control program shown as a flowchart of FIG. 6. 302 denotes a fixer control unit for turning on and offa fixer heater based on a control signal from the printer engine controlunit 301. 303 denotes a scanner control unit for controllingenergization and de-energization of the scanner motor based on a controlsignal from the printer engine control unit 301. 304 denotes a highvoltage control unit for controlling a timed sequence of the charging,development and transfer based on a control signal from the printerengine control unit 301. 305 denotes a paper feed control unit forcontrolling the spare paper feeding to stop the sheet of print paperafter passing the resist sensor, and the paper feeding to be performedfor the normal printing, based on a control signal from the printerengine control unit 301. 306 denotes a control line for transferring thecommunication between the printer controller and the printer enginecontrol unit, the image data, the print request signal, the spare feedsignal, etc. 307 to 310 denotes control lines for transferring databetween the printer engine control unit and the other various units.

A flow chart representing a sequence of spare paper feeding andsubsequent paper feeding is shown in FIG. 6.

FIG. 6 illustrates various aspects of the prior art, and, particularly,prior art apparatus having a spare paper feed function. FIG. 6 alsoincludes an illustration of a control example wherein a printer engineis connectable to a printer controller 300 without regard to any paperfeed function and such a control example is not believed to have beenknown in the art. The printer engine control unit checks whether or notit is in a print signal receivable state (S201). If the print signalreceivable state is determined, then the printer engine control unitwaits for a spare paper feed signal while waiting for a print signal(S202, S203). If the print signal is received, then the spare paper feedoperation is started and, at the same time, a paper feed jammingdetection timer is started (S212-S214). Then, the printer engine controlunit checks whether or not the resist sensor detects a sheet of paper(S215), while it also checks whether or not the paper feed jammingdetection timer is timed up in its counting (S224). If the sheet ofpaper has not reached the resist sensor before the time-up, then thecontrol flow goes to a jamming treatment (S225). If the sheet of paperhas reached the resist sensor before the time-up, then the printerengine control unit waits for a period of time To sufficient for thesheet of paper to strike against the resist roller and make a loop inthe predetermined amount (S216). Subsequently, it stops the paper feedroller and outputs a vertical synch request signal (S216-1, S217),followed by waiting for reception of a vertical synch signal (S218).Thereafter, upon receiving the vertical synch signal, the resist rolleris driven to start its rotation and the image is written completing aprinting operation (S219, S220).

If the spare paper feed signal is received prior to the reception of theprint signal (S203), then the paper feed roller is driven to start itsrotation (S204) and, at the same time, the paper feed jamming detectiontimer is started (S205). Then, the printer engine control unit checkswhether or not the sheet of paper has reached the resist sensor (S206),while it also checks whether or not the paper feed jamming detectiontimer is timed up in its counting (S207). If the timer has been timed upbefore the sheet of paper reaches the resist sensor, then the controlflow goes to a jamming treatment (S208). If the sheet of paper hasreached the resist sensor before the time-up (S206), the paper feedroller is stopped at that moment (S209), and a spare paper feed end flagis set (S210), followed by coming into a print signal standby state(S211).

If the print signal is received during that print signal standby state(S202), then the spare paper feed end flag is reset (S221).Subsequently, the printer engine control unit drives the paper feedroller to start its rotation (S222), and waits for a period of time T1sufficient for the sheet of paper to strike against the resist rollerand make a loop in the predetermined amount after passing the resistsensor (S223). Thereafter, similarly to the above normal printingoperation, the printer engine control unit outputs a vertical synchrequest signal, waits for reception of the vertical synch signal and,upon receiving the vertical synch signal, drives the resist roller tostart the printing operation.

Further, if the print request signal is not received until the elapse ofa predetermined time after one page has been completely printed, theprinter engine control unit performs a post-rotation sequence. FIG. 7shows a timing chart of primary signals generated during the process ofprinting of one sheet in a normal manner, printing another sheet withthe spare paper feeding, and coming to the stop after the post-rotationsequence. Conventionally, in the post-rotation sequence, the charge,development and transfer are turned off in this order, followed bystopping the scanner motor and the main motor. That sequence iscontrolled in the same manner even when the sheet of paper having beenpreliminarily fed remains unprinted.

However, the prior art has suffered from the following disadvantagesbecause the post-rotation sequence is performed in the same manner asthe normal printing even with the preliminarily fed sheet of paper beingin the standby state.

(1) Even when the spare paper feed signal is received in the standbystate where the feed too%or and the scanner motor are stopped whilewaiting for the print request signal and the spare paper feed signal,the sheet of paper is just fed into a predetermined position. Thus, uponreceiving the print signal, the sheet of paper is fed again afterwaiting for the scanner reached the predetermined number of revolutions.Accordingly, the control unit fails to sufficiently fulfill the functionof the spare paper feed signal delivered for the purpose of speeding upthe first printing.

(2) Delivery of the spare paper feed signal from the control unitimplies the fact that the control unit will perform printing in nearfuture. But, since the post-rotation sequence is effected to stop thescanner upon the elapse of the predetermined time after the spare paperfeeding, it is disabled to feed the sheet of paper until the scanner hasreached the predetermined number of revolutions, even with the printsignal received subsequently. This remarkably impairs the advantage ofthe spare paper feeding.

(3) In addition, the fixer temperature is switched to the standbytemperature fairly lower than the printing temperature after the stop ofthe main motor. Therefore, if the post-rotation sequence is once ended,the paper feeding must be started upon the subsequent print signal afterwaiting for the fixer temperature to reach the printing temperature, inspite of the preceding spare paper feeding.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the technical problemsas stated above.

Another object of the present invention is to provide an image formingapparatus which can increase throughput without causing such problems asincreased cost, larger consumption power, and degradation of the imagequality.

According to the present invention, the temperature of a fixer isadjusted to remain at the printing temperature in a standby statebetween two successive image forming operations. Since the fixer isalready in a fixing enable state before shifting to the next imageforming operation, it is possible to start the image forming operationat once.

Also according to the present invention, a post-rotation sequence isswitched between the case where the process enters the sequence with asheet of paper preliminarily fed being in a standby state to receive aprint signal in the apparatus and the case where a sheet of paperpreliminarily fed is not at a predetermined position within theapparatus. Thus, the advantageous effect of the spare paper feeding ismaximized to greatly contribute to an increase in throughput.

Further, according to the present invention, when a spare paper feedsignal is received in the standby state, not only is a sheet of paperjust fed to the predetermined position, but also those functions whichare necessary for the electrophotographic processes, such as driving ofa scanner and raising of a fixer temperature, which take some period oftime, are stared up. It is thus possible to more considerably speed upthe first printing in combination with the spare paper feeding, and togreatly contribute an increase of the printer function.

The above and other objects, effects and advantages of the presentinvention will be more apparent from the following description and theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an arrangement of a conventional laser beamprinter;

FIG. 2 is a block diagram of a control unit in the conventional laserbeam printer;

FIG. 3 is a timing chart of the conventional laser beam printer;

FIG. 4 is a block diagram showing a basic arrangement another typicallaser beam printer of prior art;

FIG. 5 is a block diagram showing a print control system of the laserbeam printer of FIG. 4;

FIGS. 6A and 6B are control flow charts showing a sequence of sparepaper feeding and printing operations, aspects of which are in the priorart;

FIG. 7 is a timing chart showing an operation sequence in the prior artportions of FIGS. 6A and 6B;

FIGS. 8, 8A, and 8B are control flow charts showing a sequence of sparepaper feeding and printing in a first embodiment of the presentinvention;

FIG. 9 is a timing chart showing an operation sequence in the firstembodiment of FIG. 8;

FIGS. 10, 10A, and 10B are control flow charts showing a sequence ofspare paper feeding and printing in a second embodiment;

FIGS. 11, 11A, 11B, and 11C are control flow charts showing a sequenceof spare paper feeding and printing operations in a third embodiment ofthe present invention;

FIG. 12 is a timing chart showing an operation sequence in the priorart;

FIG. 13 is a timing chart showing an operation sequence in the thirdembodiment of the present invention;

FIG. 14 is a schematic view showing an arrangement of a laser beamprinter according to a fifth embodiment of the present invention;

FIG. 15 is a timing chart of the laser beam printer according to thefifth embodiment of the present invention;

FIG. 16 is a schematic view showing an arrangement of a laser beamprinter according to a sixth embodiment of the present invention;

FIG. 17 is a block diagram of a control unit in the laser beam printeraccording to the sixth embodiment of the present invention;

FIG. 18 is a timing chart of the laser beam printer according to thesixth embodiment of the present invention; and

FIG. 19 is a timing chart of a laser beam printer according to a seventhembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment]

A first embodiment of the present invention is shown in FIG. 8. Hardwarefor implementing this embodiment can be constituted using the knownprior art shown in FIG. 5. Therefore, this embodiment will be describedbelow by referring to a control flow of FIG. 8 stored in a printerengine control unit. This control flow substantially coincides with thecontents of that explained before in connection with the prior art inthe process from the PG,21 reception of a print signal printing control.Thus, after printing the previous page (S301, S302), the elapse of apredetermined time is counted by a timer (S303). If the print signal isnot received before the elapse of the predetermined time (S304, S305),then the control flow goes into a post-rotation sequence. However, thisembodiment is different from the prior art in the control flow afterthat point.

More specifically, after entering the post-rotation sequence, thecharge, development and transfer operations are sequentially turned off,with time intervals of T_(B) and T_(C) between the former two steps andbetween the latter two steps, respectively (S306-S310). A main motor isthen turned off after a period of time T_(D) (S311, S312), followed byfinally checking for the presence or absence of a sheet of paperpreliminarily fed (S313). If it is determined that no sheet of paper ispreliminarily fed, then the control unit immediately turns off a scannermotor (S319) and comes into a print-waiting state (S320). Conversely, ifit is determined that a sheet of paper is preliminarily fed, a scannercontinues to be driven for a period of timer setting time T_(E), whilechecking the print signal (S314, S315). If the print signal is notreceived during the period of time T_(E), then the control unit turnsoff the scanner motor (S317) and comes into the print-waiting state(S318).

FIG. 9 shows a timing chart in the case where the print signal isreceived during the rotation of the scanner after entering thepost-rotation sequence under the presence of the sheet of paperpreliminarily fed (i.e., the resetting of a spare paper feed end flag).

If the spare paper feed signal is received during the writing of imagedata for the preceding page, then the printer engine control unit 301(FIG. 5) drives the paper feed roller 209 (FIG. 4) at the predeterminedtiming to feed a sheet of paper until the sheet reaches the resistsensor 211. Thereafter, if the next print signal is not received untilthe elapse of the predetermined time, then the post-rotation sequence iseffected. In this sequence, high voltage biases for the charge,development and transfer are sequentially turned off, followed byturning off the main motor after the predetermined time.

In this case, however, since the sheet of paper preliminarily fed ispresent, the scanner is not turned off, but is continued to be drivenfor a period of predetermined time. If the print signal is receivedafter a while (but before turning-off of the scanner), the main motor isdriven immediately and, at the same time, each voltage bias is raised upto a required high level. In the normal printing sequence, the paperfeed roller is started to be driven after waiting at this point for thescanner motor to reach the predetermined number of revolutions. But,since the scanner motor still continues rotating at the predeterminednumber of revolutions in this case, the paper feed roller can be drivenimmediately after the rising of each voltage bias to the required highlevel. Further, since the sheet of paper, preliminarily fed, has reachedthe position of the resist sensor, that sheet of paper can reach theresist roller in a short time to thereby start the writing of an imagequickly.

As will be apparent from the foregoing, the first printing timerequired, when the print signal is received after entering thepost-rotation sequence under a state that the sheet of paperpreliminarily fed remains in the printer, is cut down by an amountcorresponding to the time required for start-up of the scanner.

[Second Embodiment]

Next, a second embodiment of the present invention will be describedwith reference to FIG. 10.

This embodiment operates in a similar manner to the above secondembodiment shown in FIG. 8 in a sequence from the reception of the printsignal to the paper feeding, resisting and printing operation, as wellas in a sequence from the reception of the spare paper feed signal tothe paper feeding and stopping operations (S301-S312 and S319).

In this embodiment, after the high voltage biases are sequentiallyturned off and the main and scanner motors are also turned off in thepost-rotation sequence (S319), the presence or absence of a sheet ofpaper preliminarily fed is checked (S350). If the sheet of paperpreliminarily fed is absent, then the fixer is set to the standbytemperature (lower than the printing temperature) in a like manner tothe normal post-rotation, followed by a printing standby state (S356,S357). If the sheet of paper preliminarily fed is present, then thefixer is controlled to remain at a temperature higher than the standbytemperature for a period of predetermined time (S351). If the printsignal is not received during the predetermined time (S352, S353), thenthe fixer temperature is switched to the standby temperature forreturning to the normal standby state (S354, S355). If the print signalis received in a higher temperature state than the standby temperature,then the fixer temperature is controlled to rise from that temperatureto the printing temperature so that the difference therebetween iscompensated for, followed by starting the paper feeding.

With this embodiment, even after the control unit enters thepost-rotation sequence and comes into the standby state with the sheetof paper preliminarily fed being present, the fixer temperature is heldat the printing temperature or a temperature between the standbytemperature and the printing temperature for a predetermined period oftime. Accordingly, the period of time required for performing the firstprinting operation upon reception of the next print signal, can be cutdown by an amount corresponding to the period of time required for thefixer to reach the printing temperature.

[Third Embodiment]

FIG. 11 shows a third embodiment of the present invention. Hardware forimplementing this embodiment can be constituted using the known priorart shown in FIG. 5, for example. Therefore, this embodiment will bedescribed below by referring to a flow chart of FIG. 11 stored in theprinter engine control unit.

Because the flow chart of FIG. 11 is common to that of FIGS. 6A and 6Bexcept for a feature part of this embodiment, only this feature partwill be explained here.

At first, the presence or absence of the print signal is checked (S402).If yes, it is checked whether or not a sheet of paper is preliminarilyfed (S403). If the sheet of paper is preliminarily fed, then it is fedto the resist roller and vertical synchronization is performed to startthe printing control. If the sheet of paper is not preliminarily fed,then it is checked whether or not the control unit is in a standby state(S403-1). If in the standby state, the control unit enters apre-rotation (control) sequence and subsequently enters paper feedingcontrol for the printing operation.

If the spare paper feed signal is received before receiving the printsignal (S414), then it is checked whether or not the control unit is ina standby state (S414-1). If in the standby state, the scanner is drivento reach the predetermined number of revolutions (S414-2). In parallel,the paper feeding operation is started until the sheet of paper reachesthe resist sensor, followed by stopping the paper feed roller (S415,S416). At this time, the scanner remains driven (see FIG. 12). If theprint signal is received after that, then the sheet of paper is startedto be fed again after performing the pre-rotation sequence (such asrising to the high voltage biases and start-up of the fixer) other thanthe driving of the scanner. Note that S414-3 is a control step insertedfor explaining a fourth embodiment below.

FIGS. 12 and 13 show timing charts of primary signals generated whenexecuting a sequence based on the control flows of FIGS. 6A, 6B and 11.FIG. 12 is a timing chart of the prior art when the spare paper feedsignal is received in the standby state, while FIG. 13 is a timing chartin this embodiment when the spare paper feed signal is received in thestandby state. From these timing charts, the following will be found. Ina conventional timing chart where the scanner motor is not driven at thetime of starting the spare paper feeding, the control unit waits for thescanner motor to become ready after the pre-rotation sequence, followedby starting the paper feeding upon readiness of the scanner motor. Thus,a period of time T₀ is required from the reception of the print signalto the writing of an image. On the other hand, in the timing chart ofthis embodiment where the scanner motor is also driven at the time ofstarting the spare paper feeding, the paper feeding can be startedmidway in the pre-rotation sequence, and only a period of time T₁ isrequired from the reception of the print signal to the writing of animage.

[Fourth Embodiment]

In this embodiment, upon receiving the spare paper feed signal in thestandby sate, an additional step S414-3 is executed to start control ofthe fixer temperature at a high temperature (e.g., the printingtemperature) higher than the standby temperature, in addition to thedriving of the scanner motor performed in the above third embodiment. Inother words, if the scanner motor is driven upon the reception of thespare paper feed signal, the period of time taken from the reception ofthe print signal to the image writing is cut down to a large extent.Accordingly, if the fixer temperature is switched from the standbytemperature to the printing temperature upon the reception of the printsignal like the prior art, there is a fear that the fixer temperaturemay not be raised up to the printing temperature until the sheet ofprint paper reaches the fixer. This fear can be eliminated by startingto control the fixer temperature to become higher than the standbytemperature in the spare paper feeding step.

While the timing chart is similar to that of FIG. 13 shown in connectionwith the above third embodiment, the fixer temperature is started to becontrolled to the printing temperature at the same time the scannermotor is driven upon the reception of the spare paper feed signal. Theother control steps remain unchanged. However, since the printing isstarted from the condition that the scanner is already in a ready stateas stated above, the period of time T₁ in FIG. 3 is further cut downfrom the value obtainable with the above third embodiment.

As described above, when the spare paper feed signal is received in thestandby state, not only the sheet of paper is fed to the predeterminedposition, but also a feasible part of the electrophotographic process,e.g., rotation of the scanner at the predetermined number of revolutionsand possibly control of the fixer temperature to a higher temperature incombination with the former, is executed. The period of time requiredfrom the reception of the next print signal to start-up of the printingis thereby cut down to a large extent. As a result, the advantageouseffect of the spare paper feeding to increase throughput can bemaximized to greatly contribute an improvement in the printerperformance.

[Fifth Embodiment]

Next, a fifth embodiment of the present invention will be described.This embodiment is partly similar to the prior art of FIG. 1. In FIG.14, therefore, components common to those in FIG. 1 are denoted by thesame reference numerals.

Referring to FIG. 14, the surface of an electrophotographicphotoreceptor (photosensitive drum) 2 is uniformly charged by a chargeroller 5. Then, a laser beam from a laser scanner 3 irradiates thephotosensitive drum 2 through a reflection mirror 4 so that an image isexposed to create a latent image. Subsequently, toner 8 in a developer 6is applied to develop the latent image by a development roller 7. On theother hand, sheets of transfer material 13 such as paper stacked in apaper cassette 14 are fed one by one and held in a standby state with aleading end of each sheet nipped by the resist roller 11 in pair. Thesheet of transfer material 13 is then fed to a transfer roller 10 insynchronism with writing of an image onto the photosensitive drum 2. Theimage transferred to the sheet of transfer material 13 is fixed by afixer 15 comprising a fixer roller 15A having a heater therein and apressure roller 15B, following which the sheet is discharged externallyof the printer. The toner remaining on the photosensitive drum 2 afterthe transfer is cleaned by a cleaner 9. Thereafter, the image formingprocess comprised of the charging and subsequent steps is repeated.Temperature adjustment of the fixer 15 is performed by turning on andoff energization of the heater based on the temperature detected by atemperature sensor 15C. When the period of time required from start ofthe paper feeding operation to complete conversion of coded charactersor figure information, received from an external information processingapparatus into pixel information, is in excess of a certain time Tf, thephotosensitive drum 2 is stopped in its driving after the drum surfaceis charged with uniform potential by only the primary charging. On theside of the fixer 15, it waits for the end of the image developmentwhile keeping the temperature adjustment in a mode for the printing.

One example of a timing chart for the operation sequence of thisembodiment is shown in FIG. 5. In this example, coded information ofthree pages is assumed to be received in periods (a) to (b), (i) to (j)and (p) to (q) each for one page.

At first, a control unit including a microprocessor 17 starts the imagedevelopment of the coded information (i.e., the coded informationreceived in the period of (a)-(b)) for the first page. After terminatingthe reception of the coded information for the first page, a feed motoris driven at the timing (c), whereupon the photosensitive drum 2 isdriven to rotate (drum drive) and also a laser scan motor is driven(scanner rotation). Then, primary charge and transfer bias aresequentially applied to start a series of print preparatory operations,called a pre-rotation sequence, such as uniform charging over thesurface of the photosensitive drum 2 and output adjustment of the laserbeam. Afterward, at the timing (d) to synchronize the image on thephotosensitive drum 2 and the sheet of transfer material 13, the paperfeed roller 12 is driven to feed the sheet of transfer material 13 up tothe position of the resist roller 11 (paper feed pickup operation).Also, at the timing (d), the mode of the temperature adjustment of thefixer is switched from the temperature adjustment standby mode to thetemperature adjustment printing mode. Even if the image development forthe first page is completed at the timing (e), reading of the image datais not started if the pre-rotation sequence is not ended. If not,therefore, the control unit waits for the end of the pre-rotationsequence, whereupon the reading of the image data is started at thetiming (f). In this case, the period of time required for the first pagefrom the timing (d) to start the paper feed pickup operation to thetiming (e) at completion of the image development is smaller than thetime Tf, and a drum stop signal is not issued.

The laser beam from the laser scanner 3 is modulated while reading theimage data, so that the image is written onto the photosensitive drum 2.When the sheet of transfer material 13 reaches the resist roller 11, theresist roller 11 is driven to feed the sheet of transfer material 13 soas to ensure the synchronized relationship (at the timing (g) with a lagcorresponding to the difference T₁ -T₂ between the period of time T₁required for the photosensitive drum 2 to move through a distance l₁from the laser exposure position to the transfer roller 10 and theperiod of time T₂ required for the sheet of transfer material 13 to movethrough a distance l₂ (<l₁) from the resist roller 11 to the transferroller 10).

At the time the electrostatic latent image written under the laserexposure on the photosensitive drum 2 comes to the development position,the development bias is applied to develop the latent image.

After the image data for the first page are completely read at thetiming (h), the image development of the coded information for thesecond image received is started in the period (i) to (j).

In this case, since the microprocessor 17 has already received the codedinformation for the second page, the paper feed pickup operation for thesecond page is performed at the timing (k) during the reading of theimage data for the first page. With the image development for the secondpage being longer than a period of the interpaper processing time in theprinter, the sheet of transfer material 13 is nipped by the resistroller 11 and waits for the end of the image development while making aloop. At the timing (l) corresponding to the end of the imagedevelopment, the elapsed time from the timing (k) to start the paperfeed pickup operation has not reached Tf. Without issuing the drum stopsignal, therefore, the sheet of transfer material 13 is fed at thetiming (n) and the image data are read at the timing (m).

Since the microprocessor 17 has already received the coded informationfor the third page, the paper feed pickup operation for the third pageis performed at the timing (r) during the reading of the image data forthe second page. Upon completion of the reading of the image data forthe second page, the image development for the third page is started. Asto the third page, the image development is not ended after the elapseof the period Tf from the timing (r) to start the paper feed pickupoperation and, therefore, the microprocessor 17 issues the drum stopsignal at the timing (s).

In response to the drum stop signal, the transfer bias is turned off andthe surface of the photosensitive drum 2 is charged to uniform potentialby only the primary charging, following which a drive unit 30 stops thedrum at the timing (t). At this time, however, unlike the normal stop ofthe printer operation, the temperature adjustment of the fixer is notswitched to a lower temperature in the standby state, but remains at theprinting temperature.

When the image development is ended at the timing (u), the drum stopsignal is ceased at the timing (v). Thereupon, the drum is driven againto start rotation at the timing (w) and the primary charging isperformed. Since the fixer is maintained in a fixing enable state, thescanner is then started up. When the surface of the photosensitive drum2 assumes a latent image forming enable state, the resist roller 11 isdriven at the timing (y) to feed the sheet of transfer material 13 sothat the image data are started to be read at the timing (x).

Thus, if the period of time from the paper feed pickup operation to therotation of the photosensitive drum exceeds Tf, the transfer bias andthe primary charge bias are both turned off and the driving of the drumis stopped. This prevents deterioration of the photosensitive drum 2caused by charging for a long period of time, cuts and scratches on thesurface of the photosensitive drum 2 caused by the cleaner 9 duringrotation of the photosensitive drum 2 for a long period Of time,abrasion of the cleaner 9, etc. Further, since the fixer is held underthe temperature adjustment for printing, even during the stop of thephotosensitive drum 2, the print speed will not be lowered at therestart-up after completion of the image development attributable to theperiod of time required for the fixer to be heated from the standbytemperature to the printing temperature.

Now, this image forming apparatus (laser printer) has not received thecoded information after the third page, and so the paper feedingoperation for the fourth page is not performed. Thus, after the imagefor the third page has been transferred to the sheet of transfermaterial, the microprocessor performs an operation called as apost-rotation sequence where the transfer bias is turned off, thesurface of the photosensitive drum 2 is charged to uniform potential byonly the primary charging, and the sheet of transfer material 13 isdischarged externally of the printer, followed by stopping both the drumdrive and the scanner rotation. In addition, the temperature adjustmentof the fixer is returned to the lower temperature in the standby stateand the printer is stopped.

The value of Tf depends on various conditions such as the material ofthe photosensitive drum 2, the construction of the cleaner 9 and theprocess speed. For example, using an image forming apparatus comprisingthe photosensitive drum 2 comprising an aluminum cylinder of 30 coatedwith both a charge generating layer formed by dispersing aphthalocyanine dye into styrene resin as a binder and a charge carrierlayer formed by dispersing a hydrazone compound into polycarbonate resinas a binder the cleaner 9 comprising a urethane rubber blade with athickness of 2 mm and hardness of 65 degrees (JIS-A) which is inclinedto abut against the surface of the photosensitive drum 2 at an angle of22° in a direction counter to the rotation thereof, and the processspeed being 50 mm/sec, 7000 sheets of paper were printed by repeating aprinting cycle of 10 prints nines of which each include character datarequiring less than 3 seconds to complete the image development and oneof which includes character and figure data requiring more than 10minutes to complete the image development thereof. The results were asfollows. In the case of Tf=5 minutes, the urethane rubber blade of thecleaner 9 was scratched and a cleaning failure occurred. Any imagedefects due to a change in quality of the photoreceptor did not howeveroccur. In the case of Tf =3 minutes, while a cleaning failure did notoccur, the polycarbonate resin as the surface layer of thephotosensitive drum 2 was cut, which increased the electrostaticcapacity of the photosensitive drum 2 and made the primary chargingproduce an insufficient charged state, with a very slight blur on theimage but no problems in practical use. In the case of Tf=1 minute,there occurred no problems.

From the foregoing, the value of Tf is set to be 3 minutes, preferably 1minute.

When those prints taking a long period of time for the image developmentare to be printed more frequently than the above conditions, it isdesirable that the value of Tf is set to a smaller value.

Conversely, when such frequency is low, Tf may be set to a value rangingfrom 10 to 30 minutes with no problems.

As an alternative, the value of Tf may be switched between differentvalues depending on the degree of the frequency at which those printstaking a long period of time for image development occur.

Furthermore, in other eases where the surface layer of thephotosensitive drum 2 is formed of resin tending to be cut like acrylresin, the cleaning blade is formed of material susceptible to damageslike silicone rubber, or the cleaning unit employs a fur brush or aroller held in abutment against the photosensitive drum, Tf is desirablyset to a smaller value than above.

In addition, when the photoreceptor of the photosensitive drum 2 isformed of hard material such as amorphous silicon, Tf may be set to alarger value than above.

[Sixth Embodiment]

This embodiment is featured in that when the period of time requiredfrom start of the paper feeding operation to complete conversion ofcoded characters or figure information, received from an externalinformation processing apparatus, into pixel information is in excess ofa certain time Tf, which is preset to prevent deterioration of thephotosensitive drum 2 caused by charging for a long period of time, cutsand scratches on the surface of the photosensitive drum 2 caused by thecleaner 9 during rotation of the photosensitive drum 2 for a long periodof time, abrasion of the cleaner 9, etc., the driving of thephotosensitive drum 2 is stopped after the drum surface is charged withuniform potential by only the primary charging, whereas the fixer 15waits for the end of the image development while keeping the temperatureadjustment in a mode for the printing, and further after the elapse of apredetermined time Ts from the stopping of the driving of thephotosensitive drum, the temperature adjustment is returned to a modefor the standby state.

Since the above control process becomes a load on the microprocessor 17,mechanical control of the laser printer is handled by anotherindependent microcomputer 40 in this embodiment.

FIG. 16 shows an arrangement of the body of an electrophotographicprinter of this embodiment. A block diagram for control in thisembodiment is shown in FIG. 17. The configuration shown in FIG. 17 isdivided into a controller unit 100 for principally handling image(video) information, including reception of coded information of animage from an external information processing apparatus and imagedevelopment of the coded information, and a printer unit 101 forcontrolling operation of the printer body.

In FIG. 16, mechanical control on the laser printer is executed by asingle chip microcomputer 40. Loads of the microcomputer 40 include amotor driver 41, a laser scan motor driver 43, a paper feed clutch 45, aresist roller clutch 46, a sensor 47, a high voltage output circuit 48,a laser modulation circuit 49, a beam detection circuit 51, etc.Temperature adjustment of a fixer is performed by turning on and offenergization of a heater 53 based on the temperature detected by atemperature sensor 15C.

The microcomputer 40 controls the above loads in response to commandsfrom an I/O driver 23. Between the microcomputer 40 and the I/O driver23, a READY signal, a PRINT signal, a VSREQ signal, a VSYNC signal and aPRFD signal are transmitted and received. There are also prepared aserial communication line used for communicating states of the loads ofthe printer to the I/O driver 23 and communicating special commands fromthe I/O driver 23 to the microcomputer 40.

An video signal (VIDEO signal) outputted from a raster conversioncircuit 24 is applied to the laser modulation circuit 49 for modulatinga laser beam emitted from a semiconductor laser 50 in accordance withthe VIDEO signal. The modulated laser beam is scanned by a laser beamscan mirror, and the scanned laser beam impinges upon a photodiode 52disposed in a scan path of the laser beam. Then, the laser beam isconverted into a pulse signal by the beam detection circuit 51. Thepulse signal outputted from the beam detection circuit 51 is applied asa horizontal synch signal (HSYNC signal) to the raster conversioncircuit 24.

The case of receiving the coded information for the first page whichdoes take a period of a relatively short time in image development andreceiving the coded information for the second page which does take aperiod of a relatively long time in image development will now beexplained with reference to a timing chart of FIG. 18.

At first, under a condition that the printer unit 101 is powered on andheld in a state able to always receive a print signal PRINT, there is aready signal RDY. In this condition, when the controller unit 100 hascompletely received the coded information of one page in a period of (a)to (b), it sends a print signal PRINT to the printer unit 101 at thetiming (c). In response to the print signal, the printer unit 101 startsdriving of the drum and rotation of the scanner so that primary chargeand paper feed pickup are sequentially performed to be ready forreceiving the video signal. Specifically, the paper feed pickup isperformed at the timing (d) to feed the sheet of transfer material 13.Then, at the timing (e) where the leading end of a sheet of transfermaterial 13 abuts against a resist roller 11 and makes a loop, thesignal VSREQ is set true to inform the controller unit 100 of that theprinter unit 101 is now ready for receiving the video signal. In thisstate, the printer unit 101 waits for transmission of the video signal.

Meanwhile, the controller unit 100 performs the image development of thecoded information. At the timing where there is a signal VSREQ after theimage development, the controller unit 100 issues the signal VSYNC toinform start of delivering the image data. Then, the image data are readand delivered as the video signal (VDO) to the printer unit 101 in aperiod of (g) to (h).

Upon receiving the VSYNC signal, the printer unit 101 drives the resistroller 11 at the timing (i) so that the sheet of transfer material 13 onstandby is fed toward the photosensitive drum 2 in timed relation tosynchronize the leading end of the image and the leading end of sheet oftransfer material 13, thereby transferring the image to the transferroller 10.

The controller unit 100 has received the coded information for thesecond page in a period of (j) to (k) and, at the timing (l), issues aprefeed signal (PRFD) to start the paper feeding operation regardless ofthe operation of image developing means. Upon receiving the prefeedsignal, the printer unit 101 performs the paper feed pickup at thetiming (m) which can maximize the throughput of the laser printer. Then,at the timing (n) where the leading end of the sheet of transfermaterial 13 abuts against the resist roller 11 and makes a loop, thesignal VSREQ is set to inform the controller unit 100 of that theprinter unit 101 is now ready for receiving the video signal. In thisstate, the printer unit 101 waits for transmission of the video signal.

Meanwhile, the controller unit 100 performs the image development of thecoded information. In this case, since the image development is notended even after the elapse of Tf from the start timing (m) of the paperfeed pickup operation, a drum stop signal is issued at the timing (o).

Upon receiving the drum stop signal, the single chip microcomputer 40 inthe printer unit 101 turns off the primary charge at the timing (p) andmakes the motor driver 41 stop the drum drive at the timing (q).

Further, since the image development in the controller unit 100 is notyet ended even after the elapse of Ts from the stop of the drum drive,the controller unit 100 switches the temperature adjustment of the fixerto a standby mode at the timing (r).

At the timing (h) where the image development is completed, thecontroller unit 100 issues the drum stop signal and also switches thetemperature adjustment of the fixer again to a printing mode.Correspondingly, the single chip microcomputer 40 in the printer unit101 makes the motor driver 41 rotate a carrier motor 42, therebyresuming the drum drive.

Then, the single chip microcomputer 40 resumes the primary charge at thetiming (v) and, thereafter, issues the VSREQ signal upon completereadiness of the laser scanner. In response to the VSREQ signal, thecontroller unit 100 delivers the VSYNC signal to the printer unit 101,whereupon the printer unit drives the resist roller 11 so that an imagein the form of the video signal (VDO) read out of the controller unit istransferred to the sheet of the transfer material 13. After the readingof the image data, the printer unit 101 enters a post-rotation sequencein which the primary charge, the drum drive and the scanner rotation arestopped and the temperature adjustment of the fixer is switched to astandby mode, bringing the operation to an end.

The period Tf+Ts in this embodiment corresponds to a period in which thefixer is not performing the fixing operation. If this period wereprolonged, the temperature within the printer body would be raised toohigh or, in the case of using a pressure roller, its service life isaffected by the total heat amount applied thereto. In a printer designedto perform the temperature adjustment between 165° C. in a standby modeand 180° C. in a printing mode, the following was found. When the valueof Tf+Ts was more than 3 minutes, the temperature of the cleaner 9 at apoint closest to the fixer 15 exceeded the temperature in an equilibriumcondition as produced under the temperature adjustment in a standbystate. When it was over 15 minutes, that temperature was raised on theorder of 12° C. with another equilibrium condition being produced. Thetemperature rise of the cleaner 9 may invite blocking of the toner inthe cleaner and thus prevent storage of the toner, thereby causing acleaning failure. In view of the above, a continuous endurance test wasconducted on assumptions that the value of Tf+Ts was set to 15 minutesand the image used took about 15 minutes in the image development. Asthe result, a cleaning failure occurred after printing approximately4000 sheets of transfer material. On the other hand, from the result ofanother endurance test conducted on assumptions that the value of Tf+Tswas set to 5 minutes and the image used took about 5 minutes in theimage development, no abnormality was found. From the above results, itis desirable that the value of Tf+Ts is set to be about 5 minutes orless.

Incidentally, the value of Tf may be determined like the fifthembodiment.

Thus, with this embodiment, since the temperature adjustment of thefixer is once returned to a lower temperature in the standby mode forsuch data as requiring a long period of time to complete the imagedevelopment, an excessive temperature rise within the printer body willnot be caused.

Further, since this embodiment includes the controller unit 100 and theprinter unit 101 separate from each other, a sufficient degree ofextension can be provided to accommodate a host apparatus having avariety of page descriptive languages. In addition, since the controllerunit 100 can be operated with no need of considering the paper feedtiming in the printer unit 101, the control process is simplified.

[Seventh Embodiment]

This embodiment is featured in that when the period of time requiredfrom start of the paper feeding operation to complete conversion ofcoded characters or figure information, received from an externalinformation processing apparatus, into pixel information is in excess ofa certain time Tf which is preset to prevent deterioration of thephotosensitive drum 2 caused by charging for a lone period of time, cutsand scratches on the surface of the photosensitive drum 2 caused by thecleaner 9 during rotation of the photosensitive drum 2 for a long periodof time, abrasion of the cleaner 9, etc., the driving of thephotosensitive drum 2 is stopped after the drum surface is charged withuniform potential by only the primary charging, whereas the fixer 15waits for the end of the image development while keeping the temperatureadjustment remained in a mode for the printing, and further after theelapse of a predetermined time Ts from the stop of the photosensitivedrum in its driving, the temperature adjustment is shifted to a mode fora pre-standby state to keep a temperature higher than the standbytemperature but lower than the printing temperature.

FIG. 19 is a view showing a timing chart in this embodiment. Thisembodiment is operated exactly in the same manner as the aboveembodiment except for the timing of temperature adjustment. Thisembodiment is different from the sixth embodiment in that when the imagedevelopment takes a period of time beyond a certain value, i.e., itrequires more than the certain time Ts from the timing (g) to stop thedrum drive, the temperature adjustment is switched to a pre-standby modeat the timing (Y). Use of the temperature adjustment in pre-standby canreduce the period of time for the fixer to restore to a fixing enablestate when the image forming operation is started upon the end of theimage development. The print speed can be thereby increased.

One practical example is as follows. Let it be assumed that in the imageforming apparatus explained in connection with the above sixthembodiment, the apparatus uses a heat source comprising a heater of 400W, has a fixer roller comprising an aluminum core with a wall thicknessof 0.8 mm and length of 220 mm, and performs the temperature adjustmentby setting a standby temperature to 160° C., a pre-standby temperatureto 170° C. and a printing temperature to 180° C. In this case, theperiod of time required to reach the printing temperature again from thestandby temperature is about 4 seconds. On the contrary, the period oftime required to reach the printing temperature again from thepre-standby temperature is just about 2 seconds. This decrease in therequired time directly leads to a decrease in the image forming time.

The temperature adjusted in the pre-standby mode is determined dependingon a degree of temperature rise within the image forming apparatus,particularly, that of the cleaner 9 at a point closest to the fixer 15.By way of example, therefore, a continuous endurance test conducted onassumptions that the value of Tf+Ts was set to 5 minutes and the imageused took about 15 minutes in image development, while changing thepre-standby temperature. As the result, it was found that a cleaningfailure might occur when the temperature of the cleaner 9 at a pointclosest to the fixer 15 was raised in excess of about 10° C. withrespect to an equilibrium temperature in the standby mode. Note that thepre-standby temperature in this case was 176° C. It is thus believedthat in the case of setting the value of Tf+Ts to 5 minutes, thepre-standby temperature requires a setting of less than 175° C.

What is claimed is:
 1. An image forming apparatus comprising:pixelconversion means for converting coded information into pixelinformation; image forming means for forming an image on a recordingmedium based on the pixel information converted by said pixel conversionmeans; feeder means for feeding the recording medium to said imageforming means, said feeder means having a first mode in which therecording medium is fed from a recording medium stacking means forstacking recording medice prior to an end of a pixel conversion processof one page performed by said pixel conversion means, and a second modein which the recording medium is fed from the recording medium stackingmeans after the end of said pixel conversion process of one page; fixermeans for fixing the image formed by said image forming means on therecording medium; and control means for controlling a temperature ofsaid fixer means, wherein said control means executes a differentcontrol either in the first mode or in the second mode, when apredetermined time has passed after one page of an image formingoperation without starting a next page of the image forming operation.2. An image forming apparatus according to claim 1, wherein when thepredetermined time has passed after said one page of the image formingoperation without starting the page of the next image forming operation,said control means switches the temperature of said fixer means from afixing temperature to a standby temperature in the second mode.
 3. Animage forming apparatus according to claim 2, wherein when a time periodlonger than the predetermined time has passed after said one page of theimage forming operation without starting the next page of the imageforming operation, said control means switches the temperature of saidfixer means to a standby temperature in the first mode.
 4. An imageforming apparatus according to claim 1, wherein when the predeterminedtime has passed after said one page of the image forming operationwithout starting the next page of the image forming operation, saidcontrol means switches the temperature of said fixer means from a fixingtemperature to a predetermined temperature in the first mode beinghigher than that in the second mode.
 5. An image forming apparatusaccording to claim 1, wherein said image forming means comprises scannermeans for scanning a light beam modulated on a basis of the pixelinformation, and wherein after said one page of the image formingoperation without a starting of the next page of the image formingoperation, said scanner means is driven for a longer period of time inthe first mode than in the second mode.
 6. An image forming apparatusaccording to claim 1,wherein said control means starts to control saidfixer means to be a fixing temperature in synchronism with the feedingfrom the recording medium stacking means.
 7. An image forming apparatusaccording to claim 1, wherein said image forming means comprisesdeflecting means for scanning a light beam modulated on a basis of thepixel information; andwherein said deflecting means starts to be drivenin synchronism with the feeding from the recording medium stackingmeans.
 8. An image forming apparatus according to claim 1, wherein saidimage forming means comprises means for transferring an image formed onan image carrier member to the recording medium, and wherein the imagecarrier is driven after the feeding from the recording medium stackingmeans in the first mode.
 9. An image forming apparatus according toclaim 1, further comprising means for inputting the coded information,wherein the recording medium is fed from the recording medium stackingmeans in response to the input of the coded information in the firstmode.
 10. An image forming apparatus comprising:pixel conversion meansfor converting coded information into pixel information; image formingmeans for forming an image on a recording medium based on the pixelinformation converted by said pixel conversion means; feeder means forfeeding the recording medium to a predetermined position in response toa predetermined signal, prior to an end of a pixel conversion process ofone page performed by said pixel conversion means, and then feeding therecording medium to said image forming means in response to a recordrequest signal after the end of said pixel conversion process of onepage, fixer means for fixing the image formed by said image formingmeans on the recording medium; and control means for controlling saidfixer means to be maintained at a particular temperature for a fixingoperation, wherein said fixer means maintains the particular temperaturefor the fixing operation in post electrophotographic processes for alonger period of time when the recording medium is in the predeterminedposition than when the recording medium is not in the predeterminedposition.
 11. An image forming apparatus according to claim 10, whereinsaid control means starts to control said fixer means to be maintainedat the particular temperature for the fixing operation in response tothe predetermined signal.
 12. An image forming apparatus according toclaim 10, wherein said image forming means comprises deflecting meansfor scanning a light beam modulated on a basis of the pixel information;andwherein said deflecting means is driven in response to thepredetermined signal.
 13. An image forming apparatus according to claim10, wherein said image forming means comprises scanner means forscanning a light beam modulated on a basis of the pixel information, andwherein said scanner means is driven during the post electrophotographicprocesses for a longer period of time when the recording medium is inthe predetermined position than when the recording medium is not in thepredetermined position.
 14. An image forming apparatus according toclaim 10,wherein said control means has, during a period between theimage forming operation for one page and the image forming operation fora next page, a period for controlling said fixer means to assume afixing temperature included in a period where the recording mediumremains stopped in the predetermined position.
 15. An image formingapparatus according to claim 14, wherein after the end of the imageforming operation for one page, said fixing temperature controller meansswitches a temperature control mode of said fixer means from a fixingtemperature control mode to a standby temperature control modesubsequent to the elapse of a predetermined time.
 16. An image formingapparatus according to claim 14, wherein after the end of an imageforming operation for one page, said fixing temperature controller meansswitches a temperature control mode of said fixer means from a fixingtemperature control mode to a control mode for maintaining a temperaturelower than the fixing temperature but higher than a standby temperaturesubsequent to an elapse of a predetermined time.
 17. An image formingmethod according to claim 1, wherein said standby period setting step isexecuted only when a processing time required to complete saidconverting step for a next page exceeds a period of predetermined time.18. An image forming apparatus according to claim 10, wherein said imageforming means comprises means for transferring an image formed on animage carrier member to the recording medium, and wherein the imagecarrier is driven after the predetermined signal is generated.
 19. Animage forming apparatus according to claim 10, further comprising meansfor inputting the coded information, wherein the predetermined signal isgenerated in response to the input of the coded information.
 20. Animage forming apparatus according to claim 10, wherein when the recordrequest signal is generated without generating the predetermined signal,said feeder means feeds the recording medium to a predetermined positionin response to the record request signal.